The present invention relates to a seating apparatus and, more particularly, to a pressure-relieving wheelchair seating apparatus for avoidance and relief of decubitus ulcers (i.e., pressure sores).
Decubitus ulcers develop on the skin of immobilized people, particularly under bony locations like the ischial tuberosities and coccyx, when the seating pressure exceeds a typical value of 32 mm Hg for a period of time, such pressure stopping blood flow to the tissues under pressure. While other factors such as diet, moisture, and shear stress on the skin contribute to the formation of decubitus ulcers, they can generally be avoided by physically moving the immobilized person at frequent intervals to restore blood flow to the pressurized areas.
The medical industry has recognized that a general relationship exists between seating pressure and seating time. That is, the greater the seating pressure, the less time a person may sit in that same position without suffering damage to the skin and tissue located at that position. Although each person exhibits a different pressure/time relationship (based on such factors as body weight, shape and structure), a general relationship was established by J. B. Reswick and J. E. Rogers which plots the maximum suggested seating pressure vs. the maximum suggested seating time for tissue under a bony location. This relationship is commonly referred to as the Reswick/Rogers curve, and provides general seating guidelines for an average person. For example, the Reswick/Rogers curve provides that a seating pressure of 500 mm Hg will allow the immobilized person to remain seated for approximately 1.1 hours, while a seating pressure of 200 mm. H.g. will allow the immobilized person to remain seated for approximately 2 hours.
As mentioned, the seating pressure under a bony location, such as the ischial tuberosities, varies from person to person based on body weight, shape and structure. However, average seating pressures typically range from about 200 mm Hg to about 500 mm Hg. These seating pressures therefore limit the seating time to relatively short periods (i.e., 1.1 hours to 2 hours as defined by the Reswick/Rogers curve) before movement of the immobilized person is necessitated. Of course, the immobilized person can usually not move himself or herself, and must rely upon the assistance of another person.
It will be appreciated by one skilled in the medical art that typical blood pressure in the capillaries is about 32 mm Hg (0.62 psi). As a result, a seating pressure above 32 mm Hg restricts and/or obstructs blood flow in the capillaries experiencing this pressure, thus preventing blood flow to the surrounding tissues. A prolonged period of restricted and/or obstructed blood flow leads to tissue damage, and eventually to the development of a decubitus ulcer. The medical art has therefore recognized that periodic pressure relief is required (particularly a reduction in pressure below 32 mm Hg for at least five seconds thereby reestablishing capillary blood flow) with respect to body tissue experiencing pressure (e.g., seating pressure) above 32 mm Hg. However, although this requirement has been recognized by the medical art, no prior art device has been able to satisfactorily provide the necessary periodic pressure relief required by a seated immobilized person.
In this regard, the prior art has attempted to reduce the frequency of developing decubitus ulcers through the use of various seating cushions for minimizing the seating pressure under the immobilized person. For example, certain prior art cushions are provided with cut-out openings at locations corresponding to the maximum pressure points in an attempt to relieve these local pressure concentrations under the bony locations. However, the surrounding seating pressure can still be high enough to stop the blood supply in the capillaries under these bony areas. Certain other prior art cushions utilize inflatable compartments filled with air or a gel in which the pressure is alternately raised or lowered in different compartments sequentially so that the area of maximum pressure is not always in the same location. However, such prior art inflatable cushions cannot ensure that the seating pressure is adequately reduced when a particular compartment is deflated, since the deflated compartment may still remain in contact with the seated individual.
The prior art has also attempted to reduce the frequency of developing decubitus ulcers through the use of support structures including a plurality of movable elements. For example, U.S. Pat. Nos. 5,626,555 and 5,109,558 disclose support structures including a plurality of movable elements for supporting an immobilized person. The patents teach that prolonged periods of contact with a typical support structure decreases the blood circulation in the person leading to the formation of bed sores. The patents further teach that periodic relief of pressure through movement of the individual elements of the support structure can improve blood circulation and avoid soreness.
These patents, and the prior art in general, fail to recognize the complex relationship that must exist between the various aspects of a support structure for such structure to prevent development (and to actually promote healing) of decubitus ulcers. The factors to be considered include the number of individual support elements, the frequency and length of time of displacement, the sequential direction of displacement, the displacement distance of the support element, the type of cushion material, the thickness and stiffness of the cushion material, and weight, shape and bone structure of the patient, among others. A careful review of the prior art indicates that the disclosed devices fail to recognize this complex relationship and, accordingly, fail to prevent the formation of decubitus ulcers. The prior art devices are also incapable of promoting the healing of such ulcers. Finally, the mentioned prior art devices are also inadequate for retrofitting of existing wheelchairs due to their overall size and space requirements.
No single prior art seating apparatus or cushion simultaneously addresses all of the mentioned problems. There is therefore a need in the art for a seating apparatus which provides periodic pressure relief to the seated immobilized person thereby reducing the seating pressure below 32 mm Hg for at least five (5) seconds to restore and/or promote blood flow in the capillaries, which alternates this periodic pressure relief through different localities, which provides air circulation under the seated person to prevent the build-up of moisture underneath, and which allows the continued use of a wheelchair by a person with an existing decubitus ulcer.
The present invention, which addresses the needs of the prior art, relates to a seating apparatus for supporting a lower body region of an immobilized person for avoidance and relief of decubitus ulcers. The seating apparatus provides regular intervals of seating pressure reduction below a predetermined seating pressure for at least a predetermined relief period. The seating apparatus includes a plurality of rigid slats. The slats define a support plane for supporting the lower body region of the immobilized person. Each of the slats is movable between a first support position wherein each of the slats is coplanar with the support plane and a second displaced position wherein each of the slats is displaced a distance D from the support plane for the predetermined relief period whereby capillary blood pressure is reduced below the predetermined seating pressure in the unsupported portion of the lower body region. Each of the slats supports a cushion for sitting thereon, the cushion being formed from a viscoelastic material. The seating apparatus further includes a cage for supporting the slats and which is configured to allow movement of each of the slats between the first and second position. The seating apparatus further includes a plurality of mechanisms for moving each of the slats between the first and second positions. The seating apparatus further includes a controller for regulating movement of each of the slats between the first and second positions in accordance with a predetermined program. The cushion has a thickness T, a stiffness S, a maximum compression C and a recovery rate R. The thickness T and stiffness S are selected to allow the cushion to conform to the lower body region of the immobilized person to provide support therefor while minimizing an initial seating pressure Pi. The displacement D exceeds the maximum compression C. The maximum compression C is a function of thickness T, stiffness S and body weight of the immobilized person. Finally, the recovery rate R of the cushion is no greater than the predetermined relief period.
The present invention is further directed to a seating apparatus for supporting a lower body region of an immobilized person for avoidance and relief of decubitus ulcers. The seating apparatus provides regular intervals of seating pressure reduction below a predetermined seating pressure for at least a predetermined relief period and is sized and configured to retrofit an existing seat of a wheelchair. The seating apparatus includes a plurality of rigid slats having opposing ends. The slats define a support plane for supporting the lower body region of the immobilized person Each of the slats is movable between a first support position wherein each of the slats is coplanar with the support plane and a second displaced position wherein each of the slats is displaced a distance D from said support plane for the predetermined relief period whereby capillary blood pressure is reduced below the predetermined seating pressure in the unsupported portion of the lower body region. The seating apparatus further includes a generally-rectangular shaped cage having opposing sides. The cage includes a plurality of bearings located along the sides thereof. The seating apparatus further includes a plurality of mechanisms each associated with one of the slats for supporting the slats and for moving each of the slats between the first and second position. Each of the mechanisms includes a pair of support members each having first and second ends. The first ends of the support members are secured to the opposing ends of the slats. The second ends of the support members are slidably engagable with at least one of the bearings whereby each of the slats is supported by the cage. Each of the mechanisms also includes a pair of collars, each of the support members having one of the collars associated therewith. Each of the collars is fixed to the support member at a location between the first and second ends. Each of the collars includes a horizontally-disposed pin receiving slot. Each of the mechanisms also includes a drive shaft having opposing drive ends, each of the drive ends including a drive disk having a drive pin extending therefrom for engaging the horizontally-disposed slat. The drive shaft is rotatably supported by the cage and extends parallel to the slats. Finally, each of the mechanisms includes a motor operably connected to said drive shaft to impart rotational motion thereto thereby causing movement of the associated slat between the first and second position.
The present invention is also directed to a method of retrofitting a wheelchair. The method includes the steps of removing an existing seat of a wheelchair and providing a seating apparatus. The seating apparatus includes a plurality of rigid slats. The slats define a support plane for supporting the lower body region of the immobilized person. Each of the slats is movable between a first support position wherein each of the slats is coplanar with the support plane and a second displaced position wherein each of the slats is displaced a distance D from the support plane for the predetermined relief period whereby capillary blood pressure is reduced below the predetermined seating pressure in the unsupported portion of the lower body region. Each of the slats supports a cushion for sitting thereon, the cushion being formed from a viscoelastic material. The seating apparatus further includes a cage for supporting the slats and which is configured to allow movement of each of the slats between the first and second position. The seating apparatus further includes a plurality of mechanisms for moving each of the slats between the first and second positions. The seating apparatus further includes a controller for regulating movement of each of the slats between the first and second positions in accordance with a predetermined program. The cushion has a thickness T, a width W, a stiffness S, a maximum compression C and a recovery rate R. The thickness T and stiffness S are selected to allow the cushion to conform to the lower body region of the immobilized person to provide support therefor while minimizing an initial seating pressure Pi. The displacement D exceeds the maximum compression C. The maximum compression C is a function of thickness T, stiffness S and the body weight of the immobilized person. The recovery rate R of the cushion is no greater than the predetermined relief period. The method further includes the step of sitting an immobilized person on the seating apparatus and locating a pressure gauge for monitoring seating pressure on the seating apparatus at a position under the ischial tuberosities of the immobilized person. The method includes the further steps of monitoring the seating pressure under the ischial tuberosities and adjusting the stiffness S and thickness T of the cushion to reduce the initial seating pressure Pi while ensuring the displacement D exceeds maximum the compression C whereby the seating pressure is reduced to a pressure below 32 mm Hg during displacement of each of the slats. Finally, the method includes the step of installing the seating apparatus within the existing wheelchair.
Finally, the present invention is directed to a method of treating decubitus ulcers. The method includes the step of providing a chair having a seating apparatus. The seating apparatus includes a plurality of rigid slats. The slats define a support plane for supporting the lower body region of the immobilized person. Each of the slats is movable between a first support position wherein each of the slats is coplanar with the support plane and a second displaced position wherein each of the slats is displaced a distance D from the support plane for the predetermined relief period whereby capillary blood pressure is reduced below the predetermined seating pressure in the unsupported portion of the lower body region. Each of the slats supports a cushion for sitting thereon, the cushion being formed from a viscoelastic material. The seating apparatus further includes a cage for supporting the slats and which is configured to allow movement of each of the slats between the first and second position. The seating apparatus further includes a plurality of mechanisms for moving each of the slats between the first and second positions. The seating apparatus further includes a controller for regulating movement of each of the slats between the first and second positions in accordance with a predetermined program. The cushion has a thickness T, a width W, a stiffness S, a maximum compression C and a recovery rate R. The thickness T and stiffness S are selected to allow the cushion to conform to the lower body region of the immobilized person to provide support therefor while minimizing an initial seating pressure Pi. The displacement D exceeds the maximum compression C. The maximum compression C is a function of thickness T, stiffness S and body weight of the immobilized person. The recovery rate R of the cushion is no greater than the predetermined relief period. The seating apparatus has a front side and a back side. The method includes the further step of sitting an immobilized person on the seating apparatus, the person having a decubitus ulcer on a lower body region thereof. The method includes the further step of moving on an individual basis each of the slats from the first position to the second position in a sequential direction extending from the front side to the back side whereby blood flow is stimulated in the lower body region.
As a result, the present invention provides a seating apparatus which provides periodic pressure relief to the seated immobilized person thereby reducing the seating pressure below 32 mm Hg for at least five (5) seconds to restore and/or promote blood flow in the capillaries, which alternates this periodic pressure relief through different localities, which provides air circulation under the seated person to prevent buildup of moisture and which allows the continued use of a wheelchair by a person with an existing decubitus ulcer.